1. Field of the Invention
The present invention relates to an image processing method and an image processing apparatus used in an image forming apparatus and the like such as a photograph printer for reproducing a visible image such as a photographic print and the like from a photographic film on which an image of a subject is recorded by a camera, a copy machine and the like for reproducing a visible image such a photographic print and the like from a printed matter etc., and the like, wherein the image processing method and apparatus subject image information photoelectrically read out by an image reading apparatus to image processing so that the read-out image information is converted as image information which permits an image to be recorded at an image recording apparatus. More specifically, the present invention belongs to a technical field of improving an image processing method and an image processing apparatus, in which image processing such as a dodging technique and the like is carried out to remove whitening (a distant view and the like with a high luminance loses contrast and becomes white) and blackening (the face and the like of a backlighted person with a low luminance loses contrast and becomes black) by adjusting a contrast in a reproduced photographic image in a color print and the like.
2. Description of the Related Art
At present, an image recorded on a photographic film such as a negative film, a reversal film and the like (hereinafter, referred to as a film) is printed to a photosensitive material such as photographic paper and the like by so-called direct exposure in which the photosensitive material is subjected to surface exposure by being projected with an image recorded on a film, an image information recorded on a printed matter, or the like.
Recently, research of printers making use of digital exposure, that is, digital photo printers has been carried out. In the digital photo printers, after image information which has been recorded on a film, a printed matter or the like is photoelectrically read out, the read-out image information is converted as digital image information to be recorded by being subjected to various kinds of image processing. Then, a photosensitive material is scanned with and exposed to recording light which has been modulated in accordance with the digital image information to thereby record an image (a latent image) and the recorded image is developed, and thus, the photographic print is obtained.
In the digital photo printers, since a film is photoelectrically read and exposure conditions are determined after a color image density is corrected by signal processing, a period of time during which a single image is exposed is short and the exposure time is fixed to respective values in accordance with an image size. As a result, printing can be promptly carried out as compared with the conventional area exposure.
With the digital photo printers, editing such as combining of a plurality of images, division of an image, and the like, layout of printed images such as editing of characters and images, and various kinds of image processing, such as color/image density adjustment, adjustment of a conversion of magnification, edge enhancement (sharpness enhancement) and the like, can be carried out freely. Therefore, finished prints having been edited and processed freely in accordance with their use can be output. Since the images recorded on finished prints can be stored in a recording medium such as a floppy disk and the like as image information, it is not necessary to prepare a film serving as an original image when additional prints are made. Further, since it is not necessary to determine exposure conditions again, a job can be promptly and simply carried out.
In the prints made by the conventional direct exposure (areal exposure), the images (image density information) recorded on a film or like cannot be perfectly reproduced in some points such as resolution, color/density reproducibility and the like due to the limitation imposed on the reproducible image density range of photosensitive materials. However, with the digital photo printers, prints, on which the images (image density information) recorded on a film or the like are reproduced approximately perfectly, can be obtained.
Basically, the digital photo printers are composed of an image reading apparatus for photoelectrically reading out an image recorded on a document such as a film or the like, an image processing (setup) apparatus for subjecting a read-out image to image processing and determining exposure conditions for recording the image, an image recording apparatus for scanning and exposing an photosensitive material in accordance with the thus determined exposure conditions and developing the image and an image display apparatus such as a monitor or the like for displaying a reproduced print image.
The applicant has invented various image reading apparatuses and image reading methods for realizing the digital photo printer and proposed them in Japanese Unexamined Patent Publications Nos. 6-217091, 6-233052 and 6-245062. Further, the applicant has disclosed the outline of the apparatuses used to the digital photo printer in the above publications.
In the image reading apparatus used in the digital photo printers, reading light produced by a light source impinges upon a film to thereby obtain projected light which carries an image recorded on the film. The image carried by the projected light is read out by subjecting the projected light to photoelectrical conversion. As a result, the image carried by the projected light is formed to an image sensor such as a CCD sensor or the like through an image forming lens. Then, after the thus read image is subjected to various kinds of image processing when necessary, the image is transferred to the image processing apparatus as the image information (image data signals) of the film.
In the image reading apparatus for carrying out reading by, for example, slit scanning, reading light having a slit-like shape extending in a one-dimensional direction is irradiated to a film, and the film is moved in a direction, which is approximately normal to the one-dimensional direction. (Alternatively, the reading light and a photoelectric converting device are moved in the direction, which is approximately normal to the one-dimensional direction.) In this manner, the film is scanned in two-dimensional directions. An image of the light, which has passed through the film and carries the image information on the film, is formed on a light receiving face of the photoelectric converting device, such as a CCD line sensor or the like and read as a light amount data through photoelectrical conversion. The read-out light amount data is amplified and then converted into digital signals through A/D conversion. Thereafter, the digital signals are subjected to various kinds of image processing such as correction for a fluctuation in the characteristics among CCDs, image density conversion, and conversion of magnification, and the processed digital signals which are obtained through the image processing are transferred to the image processing apparatus.
The image processing apparatus sets image processing conditions in accordance with image information having been input and displays an image on a display (an image display apparatus) to which the image information is output. After the operator carries out testing and adjusts the image processing conditions when necessary, the image information is subjected to set image processing and transferred to an image recording apparatus as output image information (exposure conditions) for recording the image.
More specifically, in the image processing apparatus, for example, a visible image is reproduced from the received image signals and displayed on a display apparatus, such as a cathode ray tube (CRT) display apparatus. When necessary, the operator, who views the reproduced image, corrects the gradation, the color, the image density, or the like, of the reproduced image (i.e. sets the setup conditions). In cases where the reproduced image is judged as being acceptable as a finished print, the image information is transferred as image information to be recorded to the image recording apparatus or a monitor.
In the image recording apparatus, when it is, for example, an apparatus making use of a light beam scanning (raster scanning) exposure, three kinds of light beams corresponding to exposure of the layers, which are formed on a photosensitive material and are sensitive to three primary colors e.g., red (R), green (G) and blue (B), are modulated in accordance with the image information transferred from the image processing apparatus and deflected in a main scanning direction (which corresponds to the aforesaid one-dimensional direction). Also, the photosensitive material is conveyed in a sub-scanning direction, which is approximately normal to the main scanning direction (otherwise, the deflected light beams and the photosensitive material are relatively sub-scanned). In this manner, the photosensitive material is two-dimensionally scanned with and exposed to the light beams carrying the image (the image is printed) to thereby form a latent image, that is, the read-out image is recorded on the photosensitive material. Subsequently, the photosensitive material having thus been scanned with and exposed to the light beams is then subjected to development processing in accordance with the exposed photosensitive material. For example, in cases where the photosensitive material is a silver halide photographic material, it is subjected to the development processing comprising the steps of color development, bleach-fix, washing, drying and the like. A finished print (photograph) on which the image recorded on a film is reproduced is thereby obtained.
Incidentally, recording conditions under which an image is recorded on a film are not fixed and there are many cases where a large amount of difference exists between a bright portion and a dark portion (image densities) as found in an image recorded using an electronic flash, a backlighted scene and the like.
The photosensitive material can record an object in a comparatively wide range of luminance. However, since the maximum image density on the photosensitive material is limited, the dynamic range of image density, that is, the dynamic range of exposure which can be reproduced by the photosensitive material is narrower than the dynamic range of luminance of the object and the dynamic range of image density of a film. As a result, when a film image of a scene in which the image of an object has a large difference in luminance is exposed by a conventional method and made to a finished print, there is a tendency that details become imperceptible due to insufficient gradation in either one of a bright (highlight) portion and a dark (shadow) portion on the print. For example, in cases where a picture of a person is recorded against the light, if the picture is exposed and printed such that the image of a person may be preferably clear, the bright portion, such as a sky region, will become white and its details will become imperceptible. Whereas, if the picture is printed such that the bright portion, such as the sky region, may become preferably clear, the image of the person will become black and its details will become imperceptible.
In the conventional printer using the areal exposure, when a photosensitive material is exposed using a film image having a large difference between a bright portion and a dark portion as an original image, there have heretofore been employed a so-called dodging technique, a masking print technique and the like.
In the dodging technique, an ordinary level of exposure is given to a region having an intermediate level of image density in a scene. Also, a long time of exposure is given selectively to a region (for example, the portion of a distant view including distant mountains and the like as the background of a person), which is considered to become white and the details of which are considered to become imperceptible on the print, by using a perforated blocking plate. Further, as for a region (for example, the portion of a backlighted person), which is considered to become black and the details of which are considered to become imperceptible on the print, the exposure time is kept short selectively by using a blocking plate. In this manner, the print is obtained such that the contrast of each subject may be kept appropriate, and the details of the bright portion and the dark portion may be kept perceptible, that is, for example, a distant view and a person can be viewed with appropriate contrast. A method has been proposed, in which an unsharp image film having been photographically formed by the negative-positive reversal of an original image film is used as a blocking plate for locally controlling the exposure time, and in which the printing is carried out by superimposing the original image film and the unsharp image film on one upon the other.
The dodging technique is a method of obtaining a finished print in which a proper image is reproduced over an entire picture in such a manner that an ordinary level of exposure is carried out to a portion having an intermediate image density, an amount of exposure light is increased to a portion where an image tends to become white (a bright portion) and an amount of exposure light is reduced to a portion where an image tends to become black (a dark portion) to thereby correct a very bright portion and a very dark portion of the image recorded on film. Therefore, conventional apparatuses using the surface exposure employs the dodging technique to locally modify an amount of exposure light in accordance with an image recorded on a film. More specifically, the dodging technique uses a method of carrying out exposure by inserting a blocking plate, an ND filter or the like into an exposure light passage, a method of locally changing an amount of light produced by an exposure light source, a method of creating monochrome films by reversing the bright portion and the dark portion of an image recorded on film while making the image unsharp and carrying out exposure by superimposing the films, and the like.
On the other hand, when the dodging technique is intended to be carried out in a digital photo printer, it is very difficult to carry out exposure by inserting a dodging filter or the like into the light passage of a light beam. Thus, it is contemplated to obtain an effect similar to that achieved by dodging in such a manner that an amount of exposure light is increased at a portion where an image tends to become white and an amount of exposure light is reduced at a portion where an image tends to become black by image information processing.
In the digital photo printer, since the operator cannot carry out the dodging by selectively using a filter or the like, it is difficult to predict the effect of the dodging. Therefore, the operator cannot help confirming the effect of dodging from a finished print. As a result, when a dodging function is provided with the digital photo printer, there arises a problem that a finished print in which dodging is improperly carried out may be obtained.
Incidentally, when it is desired to obtain approximately the same degree of a dodging effect to images having a different resolution (a different size) which have been recorded from the same subject, the same degree of unsharpness must be given to the subject.
However, in the aforesaid dodging technique, since operation is carried out using an unsharp image having a fixed mask size which is prepared regardless of a size of an image to be reproduced, the same subject has a different degree of unsharpness when an image is printed in a different size or displayed on a monitor of different size and when an image has a different image density. That is, since a face of the same subject, for example, has a different degree of unsharpness, there is a problem that the effect of dodging is different depending upon a size and the dodging cannot be properly carried out at all times. In particular, there is a serious problem that when a dodging parameter is tested using an image displayed on a monitor, the image displayed on the monitor does not coincide with a print image.
Incidentally, the digital photo printer can adjust the quality of a finished print in a relatively wide range not only by the dodging technique but also by the image information processing.
As a result, it has been desired to realize an image processing method and apparatus capable of realizing a digital photo printer which can achieve the above dodging effect as well as stably obtain a finished print in which an image having good image quality is reproduced.
In view of the above circumstances, a first object of the present invention is to provide an image processing method and an image processing apparatus capable of obtaining a similar dodging effect at all times even if a reproduced image has a different size.
A second object of the present invention is to provide an image processing method and apparatus embodying the method which are capable of stably obtaining a properly finished print having good image quality with the sufficient effect of the dodging technique. The image processing method and apparatus, which are used in the aforesaid digital photo printer and the like, subject photoelectrically read out image information to image processing to thereby prepare image information for recording an image. The image processing method and apparatus are such that an image having good image quality can be recorded regardless of a state of a film as an original image by carrying out a dodging technique (image information processing for obtaining an effect similar to that obtained the dodging technique using direct exposure) as well as the operator can create a print while confirming a dodging effect.
A third object of the present invention is to provide an image processing method and apparatus embodying the method capable of reproducing an image having good image quality and stably obtaining a properly finished print regardless of a state of film as original image. The image processing method and apparatus, which are used in the aforesaid digital photo printer and the like, subject photoelectrically read out image information to image processing to thereby prepare image information for recording an image. The image processing method and the image processing apparatus discriminate states of an image recorded on a film such as over-exposure/under-exposure, backlight, photographing carried out using an electronic flash, and the like and carry out proper image information processing such as the dodging and the like.
To achieve the above first object, a first embodiment of the present invention provides an image processing method, wherein a visible image is reproduced from digital image data representing a photographic image. The method comprises the steps of:
i) preparing a plurality of kinds of low-pass filters for creating an unsharp image having a different mask size from the digital image data;
ii) selecting a low-pass filter having a mask size corresponding to the pixel density of an image to be reproduced from the plurality of types of the low-pass filters;
iii) creating unsharp image signals representing the unsharp image of the photographic image using the selected low-pass filter;
iv) obtaining difference signals by carrying out subtraction between signals relating to pixels which correspond to the digital image data and the unsharp image signals; and
v) obtaining processed image signals for reproducing visible signals by subjecting the difference signals to predetermined image processing.
It is preferable here to select a low-pass filter from the plurality of kinds of the low-pass filter having a different mask size which is suitable depending upon the size of a print to be reproduced or depending upon the size of the print to be reproduced and whether an image to be reproduced is used for the display on a monitor or not.
To achieve the above second object, a second embodiment of the present invention provides an image processing apparatus, wherein a visible image is reproduced from digital image data representing a photographic image, the image processing apparatus comprises:
i) a plurality of kinds of low-pass filters for creating an unsharp image having a different mask size from the digital image data;
ii) low-pass filter selection means for selecting a low-pass filter having a mask size corresponding to the pixel density of an image to be reproduced from the plurality of types of the low-pass filters;
iii) unsharp image signal creation means for creating unsharp image signals representing the unsharp image of the photographic image using the selected low-pass filter;
iv) subtraction means for obtaining difference signals by carrying out subtraction between signals relating to pixels which correspond to the digital image data and the unsharp image signals; and
v) image processing means for obtaining processed image signals for reproducing visible signals by subjecting the difference signals to predetermined image processing.
It is preferable here to select a low-pass filter which is suitable depending upon the size of a print to be reproduced or depending upon the size of the print to be reproduced and whether an image to be reproduced is an image used for the display on a monitor or not.
The selection of a low-pass filter having a mask size in accordance with the pixel density of an image to be reproduced means to select a low-pass filter in accordance with a xe2x80x9cprint sizexe2x80x9d to be reproduced. The terms xe2x80x9cin accordance with the print sizexe2x80x9d also means to select a low-pass filter depending upon whether an image to be reproduced is used for the display on a monitor or recorded on a print because not only a print but also an image displayed on the monitor have always a fixed size in a system using the same apparatus.
As a specific method of creating unsharp image signals, it is preferable to create the unsharp image signals in such a manner that digital pixel signals are converted into luminance signals and filtered. Further, the unsharp image signals may be created by photoelectrically reading out a projected image which is obtained by making the color image photoelectrically unsharp.
In the arrangement in which prescanning is carried out to previously measure resulting color signals, the unsharp image signals may created in such a manner that pixel data is thinned out at predetermined intervals in the prescanning to thereby create the unsharp signals of the thinned-out signals and the intervals at which the unsharp signals are thinned out are interpolated.